We keep listening to 1420 MHz even though we do not broadcast anything on that frequency (I keep seeing that frequency on my screensaver). We don't broadcast on that frequency precisely because it is the fundamental frequency of radio astronomy, and that frequency is kept clear by international regulation. Wouldn't other civilizations do the same?
Also, because it is a natural frequency, any signals we get on it might be attributed to natural phenomena, like a hydrogen maser.
Wouldn't a better choice be 1420 MHz times some mathematical constant, like the 1420 MHz*pi signal of TYC 1220-91-1? Or Euler's Constant, SQRT (2), or Golden Ratio phi?

That's a good point. Perhaps this explains why none of the early searches, confined to 1420.405MHz and the immediately surrounding frequencies, heard anything definite. The modern trend is to listen to a wide range of frequencies, so this potential problem should now be avoided.

The 1420 band is kept clear of INTENTIONAL transmissions, but there are plenty of unintentional transmissions - just think about how much effort is required to remove or blank the RFI from radars etc.Bob Smith
Member of Seti PIPPS (Pluto is a Planet Protest Society)
Somewhere in the (un)known Universe?

The above makes for not a good start here, but apparently becomes this.

But next the fact that this could be an excuse for something else, because actually I did not follow up on this thing and therefore do not know the complete answer.

A set of international agreements makes for a given transmission by humans very limited, although it may not be completely excluded either.

Rather we are assumed to believe that this frequency could be used by possible aliens, because it is the radio frequency band and therefore makes such communication possible.

The old seticlassic web pages has a page related to Promising Gaussian Candidates, sorted by means of score.

The gaussian table in SMV lists the important fields related to the gaussian score.

A SMV log being used on this computer is having some 13462 lines right now and best gaussian score is 14.525034 .

We probably could be more familiar with such things as Chinese lanterns rather than a couple of other things, but even with such things as orbs, rods, critters and so on, we still could make a
guess about the possible hammer being used rather than the feather for a couple of things.

Are we supposed to believe that any aliens or extraterrestrials could be looking much like ourselves, or perhaps only be a lump of "slime"?

Any such scores like those as the seticlassic web pages should be that of radio signals rather than something else and next we could believe that these might have come from someone.

Sorting the bg_chisq column in SMV, the chi square, or fit, never gets to or above 1.42, which should be confused with the mentioned frequency above, as far as I am able to tell.

Similarly, there could be some 4 lines in SMV for the same fit which is below 1.00 .

None of these scores tells anything about a possible alien presence, so here I rather could leave it for someone else to decide, or perhaps make to the wrong conclusion that we are not alone in space.

The idea of regulating the use of radio frequencies near 1420 MHz is that it is useful in radio astronomy, for monitoring the emissions of hydrogen, by far the most abundant substance in the universe. Monitoring this frequency has provided us with a great deal of information about the workings of the cosmos.

It's far more useful to us , in this way, than it would be as just one more channel for our own radio transmissions. For these transmissions, there are a great many such channels from which to choose. Is seems quite reasonable that other civilizations in space would also want to reserve this band of frequencies for radio astronomy.

Presumably for the same reason we do. Most of the universe is hydrogen, and hydrogen's fundamental frequency is 1420 MHz. So if the aliens are interested in astronomy (as they would likely be if they would be interested in broadcasting to us), they would want to keep this frequency clear, to observe on. Also, if you want to send a signal to an alien species (as we would be to them), I would think you would avoid frequencies characteristic of natural phenomena so the signal would not be mistaken for a natural phenomena. Instead, your frequency would be something like SQRT(2)*1420, or 1420*pi, or some other mathematical offset.
EDIT: Oh, I see someone else already answered you. Well, I still think we should pick five or six mathematical constants and divide or multiply the Hydrogen frequency by them, and look hard on those settings.

I'm trying to figure out why the radio frequency is 1420 MHz so often are used when searching for alien transmissions.
Is that band somehow better than other bands to make an carrier wave that could include any messages?

I'm trying to figure out why the radio frequency is 1420 MHz so often are used when searching for alien transmissions.
Is that band somehow better than other bands to make an carrier wave that could include any messages?

The waterhole, or water hole, is an especially quiet band of the electromagnetic spectrum between 1,420 and 1,666 megahertz, corresponding to wavelengths of 21 and 18 centimeters respectively. It is a popular observing frequency used by radio telescopes in radio astronomy. The term was coined by Bernard Oliver in 1971. The strongest hydroxyl radical spectral line radiates at 18 centimeters, and hydrogen at 21 centimeters. These two molecules, which combined form water, are widespread in interstellar gas, and their presence radiates radio noise at these frequencies. Therefore, the spectrum between these frequencies form a "quiet" channel in the interstellar radio noise background. Bernard M. Oliver theorized that the waterhole would be an obvious band for communication with extraterrestrial intelligence, hence the name, which is a form of pun: in English, a watering hole is a vernacular reference to a common place to meet and talk. Several programs involved in the search for extraterrestrial intelligence, including SETI@home, search in the waterhole radio frequencies.

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